This research project is concerned with the elucidation of the mechanism of physiologically important reactions, primarily through the use of kinetic methods. Techniques are used which permit the measurement of characteristic time constants of chemical reactions as short as 10 to the minus 10th power sec so that virtually the entire time range accessible to chemical processes can be probed. Stopped flow, temperature-jump, stopped flow-temperature jump methods and measurements of fluorescence lifetimes are used as well as more conventional techniques. A portion of this project is concerned with the further improvement and development of physical methods which can be applied to biological systems. Two important objectives of this study are the detection of reaction intermediates and the delineation of elementary steps in complex biological processes. The particular types of biological systems under investigation include metabolic control through allosteric enzymes, organized enzymes, and membranes. The structure and function of membranes are being studied in both model and physiological systems, with particular emphasis on the mechanism of action of membrane-bound enzymes and metabolic control through hormone-membrane interactions. The long term goal of this work is to understand complex biological mechanisms in terms of molecular structure.